The present invention relates to the automatic reading of a line drawing and more particularly to the automatic recognition of a drawing including a portion in which a plurality of lines of different types or kinds and/or colors extend along the same path in a mutually overlapping or superposed relation and in which a given one of the plural lines is actually drawn while the remaining overlapping line or lines are represented, respectively, by corresponding overlap symbols marked in association with the given line.
When a line pattern or drawing having an area where a plurality of lines of different line types or kinds and/or colors are drawn to extend along the same path in a mutually overlapping or superposed relation, as is the case with mask patterns employed in manufacturing LSI circuits, is to be stored in a memory of a computer, it has heretofore been common in practice that such area is manually designated by an operator with the aid of a table. For reducing the burden of the operator, it is of course desirable that the line pattern is automatically recognized with the resulting data being inputted to the computer. However, a problem arises in this connection in that the line pattern including the mutually overlapping lines is drafted in a variety of different ways in dependence on the preferance of the draftsmen. Supposing, for example, that a line of type or kind A overlaps a line of a kind B in a drawing, one draftsman may draw the pattern with both kinds (A and B) of lines being intermingled, while another draftsman may omit one line and use a symbol representing omission or overlap of that line. In other words, representation of a line pattern including mutually overlapping lines or segments differs in dependence on the draftsmen, resulting in great difficulty in the automatic recognition of line patterns.